Water guns have long been very popular toys. Most toy water guns have pumps that are manually operated, such as by a trigger that when pulled moves a piston along a cylinder in a discharge stroke to expel water from the cylinder and out through a one-way discharge valve and a discharge conduit to a nozzle. A spring moves the piston back along the piston in the opposite direction during an intake stroke in which water is drawn into the cylinder from a reservoir through a one-way intake valve and an intake conduit. The two-stroke cycle of a manually operated water gun results in an interruption of the water output; the gun shoots a small short-duration spurt of water on the delivery stroke of the piston and stops shooting upon each intake stroke of the piston.
A variant of the manually operated water gun that has enjoyed some popularity in recent years is the battery-operated water gun, which has a battery-powered motor that drives a reciprocating piston pump. The water output from battery-operated water guns is also intermittent, but the operating cycles and the delays between spurts are short so the water stream approaches that of a continuous flow. Battery-operated water guns are relatively expensive, and keeping them in batteries compounds the costs of owning one.
A very popular, relatively recent entry into the toy water gun market is the pressurized-air water gun. A manually operated air pump pumps air into a water tank. When a trigger valve is opened, the air pressure in the tank expels water from the tank through a discharge conduit and nozzle. As long as the pressure in the tank is elevated and for as long as the trigger valve is held open, the gun will shoot a continuous stream of water. As the pressure drops from a maximum, however, the strength of the emerging water stream and thus the range of the gun diminish. Maintaining a long range requires the user to operate the air pump frequently, and because it is cumbersome to keep the trigger pulled with one hand and operate the pump with the other, the gun is usually not operated simultaneously with pumping it up. In other words, the user has to interrupt his or her shooting to "reload." Air-pressurized water guns are also comparatively expensive.